The present invention relates to window coverings and, more particularly, to fabric window coverings provided with adjustable vanes for controlling the amount of light passing therethrough. The present invention also includes methods and apparatus for producing such a window covering.
Fabric window coverings are often preferred by consumers for a number of their features. The features most often considered desirable are the softer appearance relative to traditional Venetian blinds, the uniform appearance which they provide a window, and the insulating properties associated with cellular fabric shades.
Cellular fabric shades offering these features are known in the art. For example, U.S. Pat. No. 4,450,027 to Colson discloses cellular window coverings which may be made of fabric or film materials. In the process disclosed in the Colson patent, a flexible strip material is folded into a continuous longitudinal tube and the longitudinal folds thus created are permanently set by passing the tubing material around a heat setting wheel.
Adhesive is applied along one side of the flattened tubular material which is subsequently stacked by winding onto a rack having flat surfaces. The winding in this manner presses the adhesive to the next layer wound onto the rack to form a bonded unitary stack of closed tubular cells. When the ends are cut from the rack the stack may be expanded and the permanently set creases provide a neat and uniform outward appearance.
U.S. Pat. No. 4,732,630 to Schnebly discloses a modification to the Colson process described above. In the Schnebly patent a hot-melt adhesive is applied to one side of the tubular material. After the flat tubular strips have been stacked and cut, they are placed in an oven under pressure and the hot-melt adhesive is activated to bond the layers together.
Both of the above patents disclose window coverings which exhibit the desirable features discussed to this point. However, window coverings of that type lack one feature which is often desired by consumers. That feature is the ability to control the amount of light admitted through the window covering, similar to a traditional venetian blind. There have been some attempts to provide a fabric window covering with the ability to control the amount of light entering the room. However, these attempts have lacked one or more of the features discussed above and have been less than successful.
U.S. Pat. No. 3,384,519 to Froget discloses one such attempt. The window covering disclosed therein consists of two cloth layers spaced apart by movable parallel blades having each of their marginal edges heat-welded to one of the movable cloth layers. With this window covering, relative movement of the two cloth layers in a direction perpendicular to the blades changes the angle of the blade and thus controls the amount of light admitted through the article. A number of undesirable features of the Froget window covering derive from the fact that it is constructed utilizing a heat-welding a process. First, this limits the fabrics which may be utilized to thermoplastic materials. Also, heat-welding necessarily requires a melting of at least some of the fibers of the materials bonded, thus providing an uneven outer appearance along the heat-welds and producing unwanted crimps or creases in the materials, which can result in fatigue failure. Further, heat-welding is a relatively slow process which may require six or more seconds to create a bond over an extended length. This is too slow for application in high volume commercial production processes. Other drawbacks of the Froget window covering are that heat welds are limited in strength, especially at elevated temperatures experienced by an insulating type shade placed adjacent a sunlit window; and the difficulty in achieving uniformly straight heat welded joints over an extended length.
U.S. Pat. No. 2,865,446 to Cole discloses a window covering in which a long rectangular piece of fabric is doubled back upon itself and a plurality of pleated elements are placed between the folded over sheets. The pleated elements are an accordion-pleated fabric which extends when the two sides of the folded over fabric are moved relative to one another in a direction perpendicular to the accordion pleats. Such a window covering does not provide a uniform appearance because the accordion-pleated fabric located closer to the top of the window covering does not expand to the same extent as the fabric closer to the bottom of the window covering. Also, it is very difficult to ensure that such accordion-pleated fabric returns to its desired position after each expansion.
The construction of Cole inherently creates an undesirable feature if a woven type sheer fabric is used for the folded over, long rectangular piece of fabric. That undesirable feature is a moire effect or interference pattern which would result when light is viewed through the folded over fabric. The Froget window covering would also appear to have this drawback because the embodiment shown in FIG. 8 of that patent appears to show front and back fabrics of the same material.
French Patent No. 1,309,194 discloses a curtain with variable opacity. In this curtain, screen or mesh parallel sides are provided with tiltable braids therebetween. The braids are said to be attached at their edges to the sides, however, no means for attachment is specified. The drawings appear to indicate a hinged type attachment and the specification ends by stating that the difficulties of construction are substantial.
It is, therefore, an object of the present invention to provide a fabric light control window covering comprising first and second parallel sheer fabric sides and a plurality of opaque or semi-opaque vanes extending between the sheer fabric sides with the vanes being angularly controllable by relative movement of the sheer fabric sides.
Another object of the invention is to provide such a window covering which has a neat and uniform construction and outer appearance in all degrees of light control. In this respect a feature of the present invention is therefore adhesive bonding of the light control vanes to the sheer fabric utilizing linear application of the adhesive and, thus, a high degree of controllability of the adhesive application process and bonding of the vane. Such a feature provides advantages other than simply an improved outward appearance. The precisely uniform construction improves the operation of the blind by preventing warps or distortions from developing over the life of the blind.
Another object of the invention is to provide such a blind which operates with a high degree of repeatability, that is, always returns to the same appearance when closed. Thus, a feature of the present invention is attachment of the vanes to the sheer fabric sides such that the vanes tend to bias the window covering toward the minimum light admitting position. A further feature of the invention in this respect is a novel heat setting of the three layers together in order to provide a uniform and wrinkle-free shade at any temperature in subsequent use. These features allow the window covering to maintain its original shape and appearance even in the presence of temperature extremes encountered in a window environment.
A further object of the present invention is to provide methods and apparatus capable of producing the above window covering. One of the features of the present invention is adhesive bonding by means of adhesive linearly applied on the vane material. Linear application ensures a high degree of accuracy and provides uniform and straight adhesive lines. Another feature of the invention is the unique heat setting process utilizing hot and cold rollers and tension belts or hot and cold flat plates and belts to uniformly press the sandwiched fabrics during reheat setting and thus guarantee a wrinkle-free structure.
It is also an object of the present invention to provide such methods and apparatus which are suitable for high volume commercial type production. Features of the present invention which assist in this respect are adhesive bonding techniques which allow almost instantaneous bonding of the vane material and apparatus which allow for material changes without complete re-setup.
Accordingly, a fabric light control window covering according to the present invention comprises a first sheer fabric sheet, a second sheer fabric sheet disposed parallel to the first sheet, and a plurality of relatively opaque fabric strips adhesively bonded transversely between the sheet fabrics. Each strip has an edge portion bonded to the first sheet and an opposite edge portion bonded to the second sheet in a manner tending to bias the first and second sheets together. The window covering according to the present invention is movable between a closed position and an open position. The closed position is characterized by a central portion of the fabric strips being substantially parallel to the first and second sheer fabric sheets with the strips themselves being substantially planar. The open position is characterized by the central portion of the fabric strips being substantially perpendicular to the first and second fabric sheets and to the bonded edge portions of the strips themselves. Also, characteristic of this position is that portions of the strips between the bonded edge portions and central portions form smoothly curving surfaces which are free of creases or sharp fold. In an alternative embodiment, the central portions of the fabric strips are substantially flat and longitudinally extending hinge or flex points are provided parallel to the bonded edge portions.
According to a preferred embodiment of the invention the method for manufacturing such a window covering generally includes the following steps. A first line of hot-melt adhesive is applied to the narrow strip material adjacent nit one edge on one side. A second line of hot-melt adhesive is applied to the narrow strip material adjacent the opposite edge on the opposite side. The narrow strip material is then cut to lengths equal to the width of the wider sheer fabrics and the cut lengths are separated to provide a space between them sufficient to allow for a subsequent processing step. The first sheer fabric is fed at a constant rate longitudinally in a direction perpendicular to the longitudinal direction of the cut strips. The first sheer fabric is also fed over the cut strips in close proximity thereto. As the first sheer fabric is fed, a portion is preheated to a temperature sufficient to form a tack bond with the hot-melt adhesive. Then, while continuously feeding the first sheer fabric at a constant rate, a portion of the first sheer fabric is stopped directly over one of the cut strips so that the cut strip may be pressed and bonded to the first sheer fabric without smearing the adhesive. In order to move the bonded strips out of the way of the next strip, the stopped portion of the first sheer fabric is advanced at a speed greater than the constant feed rate, followed by a reversing of the direction of travel of the formerly stopped portion to position the first sheer fabric for application of the next cut strip in an overlaying relationship to the previously applied cut strip. The second sheer fabric is then fed into mating contact with the cut strips which have been bonded to the first sheer fabric, thereby forming a sandwich of three layers. Almost immediately after feeding the second sheer fabric, the sandwich is heated under uniform pressure and tension to melt and force the hot-melt adhesive into the sheer fabrics, and set the layers of the sandwich at a uniform temperature-size relationship. Finally, the fabric sandwich is cooled under uniform pressure and tension, thereby permanently bonding the sheer fabrics to the cut strips without creating warps or wrinkles. The final, permanently bonded fabric can then be cut to desired lateral widths and/or trimmed along the lateral edges thereof.
Apparatus according to the invention generally comprises means for performing the above described method. In particular, the apparatus includes an adhesive applicator means comprising a heating block for melting the hot-melt adhesive. The heating block contains a gear pump which provides melted adhesive to nozzles at a rate proportional to the speed of feeding of the strip material. The heating block also is designed to melt only a small portion of adhesive in order to prevent yellowing while maintaining an adequate adhesive flow.
Included in the present invention is a means for positioning the first sheer fabric in order to stop a portion for application of a cut strip and then reposition and stop the fabric before the application of the next cut strip while maintaining a constant feed rate for the first sheer fabric. This portion of the apparatus comprises two dancer rollers around which the first sheer fabric runs. The dancer rollers are mounted on shafts which form the pivot points of a linkage around its frame. The linkage causes the dancer rollers to act in concert and the timing of the rotation of the linkage is controlled by an appropriately shaped cam member.
A heat setting means is provided in which the sandwiched layers of the window covering pass between first and second adjacent endless belts. The belts each run across hot and cool surfaces to successively heat and cool the window covering. In one embodiment, the hot and cool surfaces are rollers and tension induced in the belts causes a pressure to be exerted on the sandwiched layers, thus maintaining the layers under constant and uniform pressure at a tension significantly less than the tension induced in the endless belts. In another embodiment, the hot and cool surfaces are flat plates disposed opposite air plenums and the pressure exerted on the sandwiched layers is due to the biasing of the belts toward the flat plates by pressurized air supplied to the air plenums. Alternatively, the hot and cool surfaces may be pairs of oppositely disposed flat plates biased against the belts. Heat setting in these manners allows the sandwiched layers to be set to a uniform temperature and size relationship to prevent distortions in subsequent use.
Also, included in a preferred embodiment of the invention is a heat setting means wherein the first endless belt passes around a hot roller and the second endless belt passes around a cool roller. The location of the belts and rollers is arranged such that the second endless belt also passes around the hot roller outside of the first endless belt and the first endless belt passes around the cool roller for short distance outside of the second endless belt. With this arrangement the sandwiched layers of the window covering may be passed between the two belts, around the hot and cool rollers.
A hot knife cutting assembly is preferably provided to cut the final fabric to desired lateral widths and/or to trim the lateral edges of the final fabric. The hot knife cutting assembly operates such that the three layer sandwich fabric is cut cleanly, without any heat sealing of the lateral edges of the individual fabric layers to one another.